Reassessment of Growth and Exploitation of Portunus trituberculatus in Laizhou Bay: Legacy of Historical Overfishing

To investigate growth trends of Portunus trituberculatus in Laizhou Bay, this study fitted the Von Bertalanffy growth model using FiSAT II based on carapace width frequency data from 2023 to 2025. Growth parameters and mortality coefficients were estimated, and natural mortality was evaluated using eight empirical formulas. A total of 2240 individuals (1117 females, 1123 males) were captured. The carapace width–weight relationships were W = 7.145 × 10−5L2.9153 (total), W = 1.208 × 10−4L2.8051 (females), and W = 3.209 × 10−5L3.0809 (males), indicating negative allometric growth in females and near-isometric growth in males. Asymptotic carapace widths (L∞) were 228.32, 227.23, and 215.25 mm; growth rates (k) were 0.43, 0.49, and 0.44; and the total mortalities (Z) were 1.41, 1.44, and 1.30 for total, female, and male, respectively. Recruitment occurred from April to August (spring–summer). Mean natural mortality (M) was 0.70, and exploitation rate (E) was 0.50. Compared with historical data, the current exploitation rate has decreased from the severely overexploited levels observed historically, approaching the commonly used MSY reference point of E = 0.50. This decline reflects the positive effects of summer fishing moratoriums and stock enhancement in reducing fishing pressure. However, this apparent stabilization in exploitation rate has not translated into biological recovery. Declining growth parameters and continued population decline indicate that the stock remains vulnerable, and current pressure may still exceed the ecosystem’s degraded carrying capacity. Future efforts should strengthen the monitoring and recovery of genetic diversity in P. trituberculatus, extend the study period of length–frequency data, and construct ecosystem models to assess the impacts of food competition and habitat changes, thereby providing a scientific basis for stock enhancement and resource assessment of P. trituberculatus in Laizhou Bay.